How to build a spaceplane with an interplanetary probe?

[LegitBro]

I can build planes, I can build a lightweight probe that can go to three planets in one trip. What I can't do is to merge the two together. can anybody show me a design or explain to me what makes a spaceplane work?

[Bothersome]

You need lots of wing surface area because in higher altitudes, there is not much lift applied to the wings.

You need "just enough" jet engine(s) to get it to the thin air at decent speeds.

You need a boost of some sort to get it into space.

Once in space, you need control methods, and a form of propulsion.

And of course, usually, you need a reason to go and the tools for the job.

Here is my latest space plane. It has PB-Ion propulsion for interplanetary travel (not test yet). Of course, it needs refueling once in space, but that's not hard. Notice the wing surface area. 1 extra ton of weight can really cost you in the amount of fuel you need to start with and how big your craft will grow. In my case the plane needed to be SSTO. If it can't get to orbit on it's own, then probably won't be able to get back to orbit from Laythe.

Edited August 11, 2014 by Bothersome
Showing pictures

[LegitBro]

I've almost completed the tech tree other than the final tier, My reason for this plane is to lower launch costs. I've also heard that smaller wing areas make for a more maneuverable craft. With a bigger wingspan I am afraid of my plane spinning out of control when trying to re enter.

[Wanderfound]

There are a few ways to do it. The tricky bit is ensuring that the plane doesn't become asymmetrically balanced once you detach the probe.

So, either a central cargo bay like this:

Or a pair of detachable probes like this (they're the "missiles" covered by procedural fairings):

I'd advise against trying to bolt them on top; it's almost impossible to maintain a balanced plane if you do that. You want the probe to be as close to CoM as possible, to minimise the change in balance after it detaches. You can also do some useful balance-maintaining trickery by pumping fuel from one tank to another.

[Wanderfound]

Also: if you haven't got any SSTO spaceplanes up and running yet, I'd advise you to just try and make something that can reach orbit before you start messing around with cargo lifters.

You should also get some use from what I've posted at http://forum.kerbalspaceprogram.com/threads/89643-SSTO-question?p=1334110&viewfull=1#post1334110

Use the example plane I've linked to there, take it for a spin to get a feel for the ascent requirements, then go into the SPH and tear the plane to pieces to see how it's built.

And, as always: if you aren't already using FAR, I'd strongly recommend it. Planes are much more fun when they actually fly like planes.

[Bothersome]

Well, I have done re-entry tests several times (mostly to test after an upgrade). I didn't have any trouble with the above plane. But I kept the nose pointed into the wind at all times. After the flames are gone, I'd give about 10 degrees up so I could keep about 8000 meters altitude to fly home. I know planes of just about any kind will flip out sometimes if you come in with crazy attitude angles. The one above does have a slight slip problem due to lack of large rudders. But rudders are really needed much for doing the heavy lifting. So I opted for not using large rudders. You can barely see them but there are four rudder control surfaces close to the engines.

The other thing to keep in mind, is that this plane was designed to also go and take off again on Duna. I know the jet engines can't be used on Duna (no oxygen). Because Duna has very thin air, you need very large wing surface area in order to fly and land at any decently slow speed. That plan can take off at about 40m/s and land at about 28m/s on Kerbin. So I'd estimate about 60m/s landing on Duna, hopefully slower.

I won't get into why my Duna mission parameters eventually changed to a rocket SSTO instead of a plane, so-as I don't pollute your thread with counter-plane ideas and arguments.

[LegitBro]

Thanks for all the comments, I learned alot! though the plane I need only has to lift about 1ton into LKO. After that the probe itself can get to almost anywhere. The plane I used is alot smaller and barely makes it to orbit.

[Wanderfound]

Thanks for all the comments, I learned alot! though the plane I need only has to lift about 1ton into LKO. After that the probe itself can get to almost anywhere. The plane I used is alot smaller and barely makes it to orbit.

http://forum.kerbalspaceprogram.com/threads/89092-Kerbodyne-Scattershot-a-simple-and-easy-to-fly-beginner-s-SSTO-spaceplane

This one can easily reach orbit with its tanks still half-full. It'd take a bit of modifying to make it into a probe-carrier, but it might be a useful place to start from. Pulling the goo pods and material bays should free up some weight capacity.

Edited August 11, 2014 by Wanderfound

[SRV Ron]

One can even consider using a turbojet as a rocket with air hogging. This design, with very careful flying on a precise path, can hit 2,400 m/sec at 36,000 meters before burnout with an apogee of 180,000 meters. The turbojet can be recovered after you stabilize the orbit of the payload but is unflyable without its payload.